Structures that Indo-European languages use to encode grammatical meaning include words (lexicon), their division into parts (morphology), and their grouping into parts of speech (word classes). Arrangements of words into sentence (syntactic) and discourse (pragmatic) structures also adds grammatical meaning.
In addition to lexical, morphological, and syntactic forms, Indo-European grammar encodes more general linguistic grammatical (semantic) categories and pragmatic priniciples such as speaker intent. Grammatical categories and pragmatic principles are encoded differently in the lexical, morphological, syntactic, and discourse structures of a language.
Over the four millennia of written Indo-European records, the expression of grammatical categories and pragmatic expressions have changed in major ways. Older Indo-European patterns of suffixes and inflectional endings were often replaced as new words, affixes (prefixes, infixes, or suffixes), and arrangements of words came to encode meaning in different ways in the later languages. Processes of change include loss of suffixes, the rise of new word classes, and changes in the status of lexical items as they came to grammaticalize older categories in new ways. The class of auxiliary verbs such as 'have, will, would', for example, come from uses of older verbs whose meaning has become grammatical (expressing past, future tense, and conditional modality).
A major problem is identifying categories that are expressed lexically at one period with morphological or syntactic expressions of another stage of language. The arrangement of Indo-European grammar here has as its long-term goal the mapping of traditional morphological categories to expressions in later languages in terms of general universal categories and their typological variants. These pages represent interactive data sets for the still evolving hypothesis formation about relations among Indo-European grammatical categories, both attested and reconstructed.